1. Field of the Invention
The present invention relates to a technology for improving an adhesiveness of an interlayer insulating film employing an insulating material having a lower dielectric constant.
2. Description of the Related Art
Needs for achieving faster operation of semiconductor devices are growing in recent years, and in order to meet the needs, investigations for reducing the interconnect capacitance are actively conducted by replacing the conventional material for interlayer insulating film of the silicon oxide film (dielectric constant K=about 4.3) to a new material having lower dielectric constant. The insulating materials having lower dielectric constant include hydrogen silsesquioxane (HSQ), methyl silsesquioxane (MSQ), organic resin materials containing aromatic compounds or the like, that have a dielectric constant of about 3, and more recently, the development of porous materials, which contains fine pores within the film for the purpose of decreasing the dielectric constant, is also investigated. Such materials having lower dielectric constant is employed for the interlayer insulating film to reduce the interconnect crosstalk, thereby achieving faster operation of the devices.
The films having lower dielectric constant generally have insufficient mechanical performances and/or plasma resistance. Thus, a protective film is often formed on the film having lower dielectric constant for the purpose of preventing damages during the processes for forming the interconnect or for depositing the insulating film.
However, the above layer constitution may cause insufficient adhesiveness between the insulating film having lower dielectric constant and the protective film.
JP-A-2001-326,222 discloses a technology of solving the insufficient adhesiveness of the insulating film having lower dielectric constant described above. FIG. 1 is a cross sectional view of an interconnect structure disclosed in JP-A-2001-326,222 as a prior art. The interconnect structure shown in the figure comprises an interlayer insulating film, which contains a silicon nitride film 1, a MSQ film 2 thereon and a silicon oxide film 4 thereon, and a copper interconnect containing a barrier metal film 5 and copper film 6, which is formed in the interlayer insulating film. Since the MSQ film 2 comprises an organic material and the silicon oxide film 4 comprises an inorganic material, the insufficient adhesion may occur between these films, and further the peeling off therebetween may be caused in the extreme cases. In order to address the problem, JP-A-2001-326,222 discloses a configuration of having a methylated hydrogen silsesquioxane (MHSQ) film 3 disposed between the MSQ film 2 and the silicon oxide film 4 as shown in FIG. 2, to improve the adhesiveness therebetween. According to the disclosure of JP-A-2001-326,222, although the MHSQ film 3 is employed in the embodiment shown in the figure, it is disclosed that other materials of polysiloxane compounds having Si—H group within their molecules may also be employed, and it is further described that the reason of improving the adhesiveness by employing these films comprising the above-mentioned materials may be considered that Si—H group is dehydrogenated to form activated reactive sites in the molecule, which, in turn, react with the upper and lower insulating films.
Nevertheless, the technology described in JP-A-2001-326,222 may have a room for further being improved in areas other than the improvement of the adhesiveness. First, the layer constitution shown in FIG. 1 may have a problem, in which it is easier to introduce moisture within the devices having such layer constitution. Although the reasons of occurring the problem is not necessarily clear, it may be considered that the surface of the MSQ film 2 is modified during the process of depositing the silicon oxide film 4 via chemical vapor deposition (CVD) to form a layer having a hygroscopic nature.
Further, the layer constitution shown in FIG. 2 may have an increased dielectric constant of the interlayer insulating film. Polysiloxane compounds having Si—H group within their molecules have a tendency to have increased dielectric constant when the compounds are exposed within plasma. It is considered that, in the layer constitution shown in FIG. 2, the surface of the film comprising polysiloxane compounds having Si—H group is modified during the deposition process of silicon oxide film 4 via CVD, thereby increasing the dielectric constant.
On the other hand, JP-A-H07-240,460 (1995) discloses a configuration, in which a silicon oxide film is deposited on a spin-on glass (SOG) film comprising hydrogen silsesquioxane via plasma CVD. It is further described that this configuration relaxes the stress in the interlayer insulating film including the SOG film, thereby inhibiting the generation of the cracks.
This configuration may also cause the increase of the dielectric constant of the interlayer insulating film. As described later, hydrogen silsesquioxane generally have a cage-shaped molecular structure as shown in FIG. 3, and there is a stronger tendency that hydrogen atom in the molecular structure is easily eliminated to increase the dielectric constant thereof. It is considered that, in the layer constitution described in JP-A-H07-240,460, the surface of the film comprising polysiloxane compounds is exposed within plasma during the deposition process of silicon oxide film, thereby increasing the dielectric constant.
Meanwhile, the method of inhibiting the deterioration of the performances due to introducing moisture within the interlayer insulating film generally employs a manner of providing a guard ring. Paragraphs 0002 and 0003 of JP-A-H10-199,883 (1998) and JP-A-2002-134,506 disclose semiconductor devices having guard rings provided therein. The guard ring in the semiconductor device is formed to surround a semiconductor chip or a specified pattern for the purpose of protecting the semiconductor chip or the specified pattern to inhibit the introduction of moisture into the semiconductor device, thereby stabilizing the operation of the semiconductor device. The introduction of moisture into the semiconductor device may cause an erosion of the metal interconnects or degrade the performances of the device by the uptake of moisture, thereby considerably deteriorating the reliability of the device. Thus, as described in the paragraph 0002 of JP-A-H10-199,883, the formation of the guard ring is an essential subject matter.
The guard ring can be provided by forming a bit line contact hole and filling the formed contact hole with a guard ring-forming material during the process of manufacturing the semiconductor device. Alternatively, in place of forming the bit line contact hole, the guard ring may also be provided by forming a node contact hole, a metal contact hole and a via contact hole that are formed therein, and thereafter filling the formed contact holes with a guard ring-forming material. Further, the guard ring may also be formed by additionally forming a dummy contact hole on the periphery of the above-mentioned contact holes, and thereafter filling the formed dummy contact holes with a guard ring-forming material. However, the configuration of providing the guard ring has reduced areas, on which devices are formed, and therefore the presence of the guard ring may be a factor of inhibiting the higher integration.